Door assemblies for SIR airbag-type systems typically include a substrate, often of ductile metal, having a door section, a mounting section for attachment to the support structure of the vehicle, and an intermediate hinge section that enables the door section to swing outwardly about the hinge upon deployment of the airbag through the deployment opening. A decorative outer skin layer is provided having an outer so-called "Class A" surface that is seen by the occupants of the vehicle. Foam plastic (e.g. polyurethane) is injected in a flowable state between the substrate and the outer skin through an opening in the door section whereupon it flows throughout the space and expands to fill the space with the foam. The foam is provided not only to cushion the door assembly for safety reasons, but also to provide a smooth backing for the outer skin so that any imperfections of the substrate do not show through on the Class A surface of the outer skin.
Difficulties have been encountered in applications where the door section is formed with reinforcing ribs that leave deep depressions in the exterior surface of the door section. In such cases, the foam in the depressed regions is caused to develop with relatively less density than that in the adjacent non-depressed regions and, over time, results in the depressions "showing through" on the Class A surface as a slightly sunken soft spot. In such cases, then, the foam does not adequately serve its function of concealing the irregularities of the door section to prevent them from being transferred to the Class A surface of the outer skin.